The invention relates to an A/D conversion device having an analog input intended to receive an analog input voltage, a reference input to which a reference voltage must be applied, and a digital output intended to supply a digital signal resulting from the conversion of the analog input voltage, comprising:
an amplifier having a first input connected to the analog input via a coupling capacitor and to the reference input via a coupling resistor, a second input connected to a power supply terminal via a storage capacitor, and an output intended to supply a signal resulting from the amplification of the difference between the signals received at the first and second inputs, PA1 an A/D converter having an analog input connected to the output of the amplifier and an output constituting the output of the device, PA1 a regulation control module comprising a controllable current source connected to the storage capacitor and allowing the voltage at the terminals of said capacitor to be varied, and a first comparator intended to perform the comparison between a predetermined regulation signal and a signal which is representative of the output signal of the amplifier, and to supply a signal allowing control of the conduction of the current source, the regulation module being active when the analog input voltage has a reference threshold.
In a device of this type, the first input of the amplifier receives a voltage whose DC component, referred to as average DC component, is equivalent to an average of the voltage level variations of the reference thresholds in the analog input voltage. The second input of the amplifier receives the voltage at the terminals of the storage capacitor. The difference between said voltage and the average DC component is adjusted in such a way that the output signal of the amplifier has reference thresholds whose voltage levels are constant and determined by the regulation signal. In the case of a variation of the average DC component, the regulation module is used for adjusting the value of the voltage at the terminals of the storage capacitor in such a way that the voltage level of the reference thresholds of the output signal of the amplifier remains unchanged. The amplitude of the variation of the average DC component may be considerable. The instantaneous values of the potentials of the dynamic signals constituting the AC component of the signal at the first input of the amplifier and representing the information which is the object of the conversion have thus a large variation amplitude, which may go beyond the admissible input range of the amplifier and lead to a saturation of this amplifier, thus causing a clipping and loss of information.